Valve gate assembly

ABSTRACT

A valve gate assembly for regulating a flow of molten material into a mold. The valve gate assembly includes a movable valve that can be positioned between a fully closed position and a fully open position. The valve gate assembly further includes an actuating system operatively cooperating with the valve to move the valve and infinitely position the valve between the fully closed position and the fully open position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.11/888,584, filed Aug. 1, 2007, now U.S. Pat. No. 7,588,436 which is acontinuation-in-part of U.S patent application Ser. No. 11/447,718 filedon Jun. 6, 2006, now U.S. Pat. No. 7,275,923 which is a continuation ofU.S. patent application Ser. No. 10/985,227 filed on Nov. 10, 2004 (nowU.S. Pat. No. 7,121,820), which claims the benefit of ProvisionalApplication No. 60/519,312, filed on Nov. 11, 2003. The disclosures ofthe above applications are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to valve gates and, moreparticularly, to a valve gate assembly for regulating a flow of moltenmaterial into a cavity of a mold.

BACKGROUND OF THE INVENTION

Injection molding is a widely known manufacturing process used toproduce a variety of parts. Injection molding involves introducing amolten material, for example a molten plastic or resin, into a cavitywithin a mold until the cavity is filled. The molten material hardens orcures in the mold in the shape of inner surfaces of the cavity. Afterthe molten material hardens or cures, the hardened or cured material isremoved from the cavity.

For injection molding, a manifold is typically used for conveying moltenmaterial from a central injection portion or sprue to a number ofcavities or to multiple points within one large cavity of the mold. Anexample of such a manifold is disclosed in U.S. Pat. No. 4,964,795 toTooman. In that patent, a manifold has a passageway through which amolten material may pass. The terminal end of the passageway, called agate, is in fluid communication with the cavity of the mold.

In addition, a valve gate is typically used with the manifold toregulate the flow of molten material into the cavity of the mold. Anexample of such a valve gate is disclosed in U.S. Pat. No. 4,173,448 toRees et al. In that patent, a valve gate is disposed adjacent the gateand includes a valve rod or pin partially disposed within the passagewaythat has a terminal end positioned such that it closes the gate andprevents the flow of molten material through the gate. However, the pincan move axially away from the gate and, as it moves farther away fromthe gate, the flow of the molten material through the gate increases.

It is known to provide an actuator to move the pin of the valve gate.Typically, the actuator is of a pneumatic or hydraulic type. Theactuator moves the pin of the valve gate from a fully closed position toa fully open position. In the fully open position, the pin is positionedaway from the gate, and molten material flows out the passageway throughthe gate into the cavity of the mold. When the cavity is full, the pinof the valve gate is moved to the fully closed position, therebyplugging the gate and stopping the flow of the molten material out ofthe passageway into the mold.

One disadvantage of the above-described valve gates is that thepneumatic actuator requires air valves because air is inconsistent inpressure. Another disadvantage of the valve gates is that the hydraulicactuator may leak oil, which is undesired. Yet another disadvantage ofthe valve gates is that the pin can only be positioned at the fully openposition or at the fully closed position, and cannot be positionedbetween these two positions. A further disadvantage of the valve gatesis that they are relatively slow and not very accurate in positioning ofthe pin.

Therefore, it is desirable to provide a new valve gate that can beinfinitely positioned between a fully opened and fully closed position,providing greater control over the flow of molten material into a mold.It is also desirable to provide a valve gate that has an actuator thateliminates the use of pneumatics or hydraulics. It is further desirableto provide a valve gate that has relatively fast actuation and accuratepositioning. Therefore, there is a need in the art to provide a valvegate that meets these desires.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a valve gate assembly for aninjection molding machine which regulates the flow of molten materialinto a mold with precision. The valve gate assembly includes a movablevalve that can move between a fully closed position and a fully openposition. The valve gate assembly further includes an actuating systemoperatively cooperating with the valve to move the valve and infinitelyposition the valve between the fully closed position and the fully openposition.

One advantage of the present invention is that a valve gate assembly isprovided for regulating a flow of molten material into a mold with morecontrol over the molding process. Another advantage of the presentinvention is that the valve gate assembly can infinitely adjust theposition of the valve during the molding process, thereby adjusting theflow rate of the molten material into the mold. Yet another advantage ofthe present invention is that the valve gate assembly has fastadjustment of the valve and accurate adjustment of the valve to 0.001inches. Still another advantage of the present invention is that thevalve gate assembly eliminates the use of hydraulics, therebyeliminating oil leaks into the mold. A further advantage of the presentinvention is that the valve gate assembly eliminates the use ofpneumatics, thereby eliminating air valves. Yet a further advantage ofthe present invention is that the valve gate assembly is consistent andnot controlled by pressure.

According to the present invention, there is provided a valve gateassembly having a valve operably associated with a valve gate of aninjection molding manifold. An actuator assembly is operably coupled tosaid valve. The actuator assembly includes an outer member coupled to anaxially moveable output shaft through a transmission assembly. Relativerotation between the outer member and the output shaft translatesthrough the transmission assembly for driving the valve and opening thevalve gate.

Other features and advantages of the present invention will be readilyappreciated, as the same becomes better understood, after reading thesubsequent description taken in conjunction with the accompanyingdrawings.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a fragmentary perspective view of a valve gate assembly,according to the present invention, illustrated in operationalrelationship with a manifold assembly and a mold;

FIG. 2 is an elevational view of one embodiment of an actuating system,according to the present invention, of the valve gate assembly of FIG.1;

FIG. 3 is an elevational view of another embodiment of an actuatingsystem, according to the present invention, of the valve gate assemblyof FIG. 1;

FIG. 4 is a sectional view along the axial length of an alternateembodiment of an actuator assembly in accordance with the presentinvention;

FIG. 5 is a sectional view taken along line 5-5 of FIG. 4;

FIG. 6 is an enlarged detailed view of a portion of FIG. 4;

FIG. 7 is a sectional view along the length of another alternateembodiment of an actuator assembly in accordance with the presentinvention;

FIG. 8 is a sectional view taken along line 8-8 of FIG. 7;

FIG. 9 is an enlarged detailed view of a portion of FIG. 7;

FIG. 10 is a sectional view along the linear axial length of anotherembodiment of an actuator assembly in accordance with the presentinvention;

FIG. 11 is an enlarged detailed view of a portion of FIG. 10;

FIG. 12 is a functional block diagram of a preferred actuator assemblyincluding a feedback position sensor constructed according to theprinciples of the present invention; and

FIG. 13 is a sectional view taken along the axial length of anembodiment of an actuator assembly shown in FIG. 12.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

Referring to the drawings, and in particular FIG. 1, one embodiment of avalve gate assembly 10, according to the present invention, is shown fora manifold assembly, generally indicated at 12, and a mold, generallyindicated at 14. The mold 14 has a first mold half 15 and a second moldhalf (not shown) defining a cavity 16 therein. The mold 14 also has atleast one, preferably a plurality of openings 18 extending through thefirst mold half 15 and fluidly communicating with the cavity 16. Itshould be appreciated that, when a molten material (not shown) isintroduced into the cavity 16 via the openings 18, the mold 14 containsthe molten material, and when the molten material hardens or cures, itholds a shape similar to that of the cavity 16. It should also beappreciated that the mold 14 is conventional and known in the art.

The manifold assembly 12 includes a manifold 20 having a manifold flowpassage 22. The manifold assembly 12 also includes at least one,preferably a plurality of nozzles 24 extending downwardly from themanifold 20 and having a nozzle flow passage 26 fluidly communicatingwith the manifold flow passage 22. The manifold assembly 12 furtherincludes a sprue 28 extending radially outward from the manifold 20 forfacilitating the introduction of molten material into the manifold 20.The flow passages 22 and 26 can be of any appropriate shape. The nozzleflow passage 26 narrows and terminates at a gate 30. As illustrated inFIG. 1, the mold 14 is positioned such that the gate 30 is positionedadjacent a respective opening 18 of the mold 14 to allow the nozzle flowpassage 26 to be in fluid communication with the cavity 16. The valvegate assembly 10 cooperates with the gate 30 of the manifold assembly 12to control the flow of molten material from the manifold assembly 12 tothe mold 14. It should be appreciated that, although more than one valvegate assembly 10 may be used with the manifold assembly 12, only onevalve gate assembly 10 is used with one gate 30 of the manifold assembly12. It should also be appreciated that the molten material may be of aplastic, metal, wood fibers and plastic, etc. and is injected into thesprue 28 of the manifold assembly 20 from a molding machine (not shown).It should further be appreciated that the manifold assembly 12 isconventional and known in the art.

The valve gate assembly 10, according to the present invention, includesa moveable valve, generally indicated at 31, for regulating the flow ofmolten material into the cavity 16 of the mold 14. In one embodiment,the valve 31 is a pin or rod-like member 32 cooperating with the gate 30to regulate the flow of molten material into the cavity 16 of the mold14. In the embodiment illustrated, the pin 32 is axially aligned withthe gate 30 and is at least partially disposed within the nozzle flowpassage 26. The cross section of the pin 32 is preferably smaller thanthe cross section of the flow passage 26 such that the molten materialmay flow around the pin 32. The pin 32 includes an end 34 that opens andcloses the gate 30 in a manner to be described. It should also beappreciated that the pin 32 is conventional and known in the art.

The pin 32 can move axially within the flow passage 26 toward and awayfrom the gate 30 in a manner to be described. The pin 32 can bepositioned in a fully open position (i.e., at the top of its stroke),wherein its end 34 is positioned away from the gate 30. The pin 32 canalso be positioned in a fully closed position (i.e., at the bottom ofits stroke), wherein its end 34 is positioned within the gate 30.Preferably, the size of the end 34 is complementary to that of the gate30, allowing the end 34 to block and substantially seal the gate 30 whenthe pin 32 is in its fully closed position. As such, when the pin 32 isin the fully closed position, it seals the gate 30 and molten materialwill not flow therethrough. When the pin 32 is in the fully openposition, molten material will flow through the gate 30 into the mold14. It should be appreciated that the pin 32 can move between the fullyclosed and fully open positions and can be stopped at any positiontherebetween in a manner to be described. It should also be appreciatedthat the molten material flow through the gate 30 increases as the pin32 moves from the fully closed position to the fully opened position.

The valve gate assembly 10 also includes an actuating system 36,according to the present invention, operatively cooperating with the pin32 for moving the pin 32 between the fully closed and fully openpositions. In the embodiment illustrated in FIG. 2, the actuating system36 includes an actuator 38 operatively attached to the pin 32. Theactuator 38 axially or linearly moves the pin 32 away and toward thegate 30. The actuator 38 can infinitely position the pin 32 between thefully closed and fully open positions, meaning that the pin 32 can cometo rest at the fully closed position, the fully open position, andanywhere in between. In one embodiment, the entire range of movement(i.e., stroke) of the pin 32 between the fully closed and fully openpositions is approximately one inch. This infinite movement can occurincrementally. For example, in one embodiment, the actuator 38incrementally moves the pin 32 a predetermined amount such asapproximately 0.001 inch increments. By axially moving the pin 32, theactuating system 36 can seal and unseal the gate 30 as discussed ingreater detail below. It should be appreciated that the actuator 38 maybe a linear motor, brushless direct current (DC) motor, linearsynchronous motor, linear drive, linear servo, or linear tubular motoror actuator for changing rotary motion to linear actuation of the pin32. Additionally, a transmission assembly which translates relativerotation between two members into linear motion is preferably utilizedin the present invention. Also, gear reduction transmission such asplanetary gear systems or the like are within the scope of the presentinvention providing infinite movement. It should also be appreciatedthat the actuator 38 may be of an electromagnetic, earth magnetic, orelectric type. It should further be appreciated that, as the incrementbecomes smaller, the positioning or movement of the pin 32 becomesinfinite.

In the embodiment shown in FIG. 2, the actuator 38 is of a linearinduction motor type. The actuator 38 includes a core 39 disposed aboutand connected to the pin 32 at an upper end thereof. The actuator 38also includes at least one, preferably a plurality of permanent magnets40 disposed axially and circumferentially about the core 39. Thepermanent magnets 40 are axially spaced by non-magnetic insulatingmembers 41 disposed axially and circumferentially about the core 39. Theactuator 38 includes a cylindrical housing 43 disposed about thepermanent magnets 40 and the insulating members 41. It should beappreciated that the pin 32, core 39, permanent magnets 40, insulatingmembers 41, and housing 43 move as a single unit.

The actuator 38 includes at least one, preferably a plurality ofelectromagnets 42 spaced axially and disposed circumferentially aboutthe permanent magnets 40. The actuator 38 also includes an electricalconnector 44 electrically connected to the electromagnets 42 and asource of power such as a controller 46 to be described. The actuator 38includes a cylindrical housing 45 a disposed about the electromagnets 42and an upper end plate 45 b closing one end of the housing 45 a and alower end plate 45 c closing the other end of the housing 45 a. Theelectrical connector 44 is connected to the upper end plate 45 b bysuitable means such as a fastener 44 a. It should also be appreciatedthat, when the electromagnets 42 are in the correct position relative tothe permanent magnets 40, the electromagnets 42 are energized by thecontroller 46 and repel the permanent magnets 40 to move the core 39 andpin 32 linearly.

The actuator 38 includes a plate 47 at a lower end for attachment to themanifold 20. The plate 47 has a locator 48 extending axially therefromfor locating the plate 47 relative to the manifold 20. The locator 48has an aperture 49 extending axially therethrough through which the pin32 extends. The locator 48 is located in a recess 50 of the manifold 20and the plate 47 is attached to the manifold 20 by suitable means suchas fasteners 51 a. The plate 47 is attached to the lower end plate 45 cby suitable means such as fasteners 51 b. The actuator 38 includes amoveable plate 52 at an upper end thereof. The plate 52 is attached tothe upper end of the pin 32. It should be appreciated that theelectromagnets 42 and plate 47 are fixed relative to the manifold 20.

The actuating system 36 also includes an encoder 54. The encoder 54 maybe of any appropriate type, including linear and rotary encoders. Theencoder 54 may employ any appropriate position sensing mechanism. In oneembodiment, the encoder 54 includes a sensing device 56 such as aphotodetector. The encoder 54 is attached to the movable plate 52 suchthat the encoder 54 travels with the pin 32. Also, the sensing mechanism56 is fixedly attached to the actuator 38 and disposed parallel to thetravel of the pin 32. As such, when the pin 32 moves, the encoder 54moves relative to the sensing mechanism 56 and detects the change inposition as the encoder 54 travels linearly. The sensing device 56translates the change in position (i.e., the position of the pin 32) toan electronic encoder signal. It should be appreciated that the sensingdevice 56 is electrically connected to the controller 46 to bedescribed.

The actuating system 40 further includes a controller 46 electricallyconnected to the sensing device 56 and the actuator 38. The controller46 receives the encoder signals and translates these encoder signalsinto a control signal. The controller 46 sends these control signals tothe actuator 38 to energize and deenergize the electromagnets 42 of theactuator 38, thereby causing the actuator 38 to move the pin 32 towardor away from the gate 30. It should be appreciated that the controller46 may be any suitable type of computer, for example, a personalcomputer (PC) or a programmable logic controller (PLC).

The valve gate assembly 10 includes an input device 58, such as akeyboard, electrically connected to the controller 46. With the inputdevice 58, a user can manually input information to the controller 46,such as the desired position of the pin 32.

In operation, the molding process can begin with the pin 32 in the fullyclosed position such that the molten material in the manifold assembly12 is prevented from flowing into the cavity 16 of the mold 14. When itis determined to allow molten material into the cavity 16 of the mold14, the controller 46 sends control signals to the actuator 38 toenergize and de-energize the electromagnets 42 to repel the permanentmagnets 40 and move them linearly, which actuates the pin 32 and movesthe end 34 of the pin 32 linearly away from the gate 30. The sensingmechanism 56 detects the change in position of the pin 32 via theencoder 54, and feeds back encoder signals to the controller 46. Whenthe pin 32 reaches the desired position, the controller 46 receives thecorresponding encoder signals and the controller 46 stops sendingcontrol signals to the actuator 38, thereby stopping the actuator 38from actuating. When the pin 32 is in the desired open position, themolten material flows through the passageway 26 and gate 30 and into thecavity 16 of the mold 14. It should be appreciated that the actuator 38can infinitely position the pin 32 anywhere between the fully closed andfully open positions and allows for quick and accurate adjustment of theflow of molten material into the cavity 16 of the mold 14.

Referring to FIG. 3, another embodiment, according to the presentinvention, of the actuating system 36 is shown. Like parts of theactuating system 36 have like reference numerals increased by onehundred (100). In this embodiment, the actuating system 136 includes theactuator 138 operatively attached to the pin 132. The actuator 138 is ofa linear motor type. The actuator 138 includes a core 139 disposed aboutand connected to the pin 132 at an upper end thereof. The actuator 138includes a rotatable nut 160 and a hollow ball screw 162 connected tothe core 139 and threadably engaged with the nut 160 for cooperatingwith the nut 160. The actuator 138 also includes at least one,preferably a plurality of electromagnets 142 spaced axially and disposedcircumferentially about the core 139. The actuator 138 also includes anelectrical connector (not shown) electrically connected to theelectromagnets 142 and a source of power such as a controller 146. Theactuator 138 includes a cylindrical housing 145 a disposed about theelectromagnets 142 and an upper end plate 145 b closing the upper end ofthe housing 145 a. The upper end plate 145 b is connected to the housing145 a by suitable means such as fasteners 144 b.

The actuator 138 includes a plate 147 at a lower end for attachment tothe manifold 20. The plate 147 has a locator 148 extending axiallytherefrom for locating the plate 147 relative to the manifold 20. Thelocator 148 has an aperture 149 extending axially therethrough throughwhich the pin 132 extends. The plate 147 is attached to the housing 145a by suitable means such as fasteners 151 b.

The actuating system 136 also includes an encoder 154. The encoder 154is a rotary encoder. The encoder 154 includes a sensing device 156 suchas a photodetector. The encoder 154 is attached to the rotatable nut160. Also, the sensing mechanism 156 is fixedly attached to the actuator138. As such, when the nut 160 rotates and the pin 132 moves, theencoder 154 moves relative to the sensing mechanism 156 and detects thechange in position as the encoder 154 rotates. The sensing device 156translates the change in position (i.e., the position of the pin 132) toan electronic encoder signal. It should be appreciated that the sensingdevice 156 is electrically connected to the controller 146.

In operation, the molding process can begin with the pin 132 in a fullyclosed position such that molten material in the manifold assembly 12 isprevented from flowing into the cavity 16 of the mold 14. When it isdetermined to allow molten material into the cavity 16 of the mold 14,the controller 146 sends control signals to the actuator 138 to energizeand de-energize the electromagnets 142 to rotate the nut 160. Rotationof the nut 160 moves the ball screw 162 linearly, which actuates the pin132 and moves the end 134 of the pin 132 linearly away from the gate 30.The sensing mechanism 156 detects the change in position of the pin 132via the encoder 154, and feeds back encoder signals to the controller146. When the pin 132 reaches the desired position, the controller 146receives the corresponding encoder signals and the controller 146 stopssending control signals to the actuator 138, thereby stopping theactuator 138 from actuating. When the pin 132 is in the desired openposition, the molten material flows through the passageway 26 and gate30 and into the cavity 16 of the mold 14.

Accordingly, the valve gate assembly 10 provides the user with morecontrol during the molding process by allowing the pin 32, 132 positionto be infinitely adjusted. For example, a molding process may be workingeffectively; however, environmental changes or wear in the mold mightrender that process less effective. The valve gate assembly 10 of thepresent invention allows the user to make changes to the process (i.e.,changes in pin position or actuation timing), thereby maintaining theproduction of quality parts.

Another embodiment of an actuator assembly 36 a in accordance with thepresent invention is shown in FIGS. 4-6. The actuator assembly 36 aincludes a portion of the pin 32 which extends into the actuatorassembly 36 a to function as an output shaft 164. A transmissionassembly, generally indicated at 165, is provided for transmittingrelative rotation between the output shaft 164 and the housing 172 intolinear motion of the output shaft. The transmission assembly 165includes a plurality of transmission rollers 166. The actuator assembly36 a also includes an electric motor assembly 168 (including a stator170), and a housing assembly 172. The motor assembly 168 moves theoutput shaft 164, by way of the transmission assembly 165, into apre-selected position, between a retracted position (shown in FIG. 4)and an extended position (not shown). The motor assembly includes anelongated cylinder 174 formed of a magnetic material rotatably supportedrelative to the housing assembly 172. Magnets 176 are mounted about anouter surface of the cylinder 174 to form an armature (with the cylinder174) within the motor assembly 168. The stator 170 is attached to andsupported by the housing assembly 172 and encircles the cylinder 174. Anexternal control wire 178, which is connected to an external controller(not shown) of any known type, selectively energizes the stator 170 torotate the armature (clockwise or counterclockwise).

The transmission assembly is provided by the elongated cylinder 174which includes a central threaded bore 180. The threads of bore 180 areengaged by the transmission rollers 166. The output shaft 164 is coupledwith the transmission rollers 166 by way of the annular rings 182 of thetransmission rollers engaging a series of corresponding annular grooves184 in the output shaft 164. The transmission rollers engages threadedbore 180 and annular grooves 184 to move along threaded bore 180 duringrotation of the cylinder 174. Thus, the elongated cylinder 174 forms adrive cylinder within the actuator assembly 36 as well as forming thearmature of the motor assembly 168. Accordingly, the elongated cylinder174 is referred to herein as the armature drive cylinder.

The output shaft 164 and the transmission rollers 166 are axiallyaligned within the threaded bore 180 of the armature drive cylinder 174.The transmission rollers 166 are spaced around a portion of the outputshaft 164 (see FIG. 5) and include a plurality of annular ribs, rings182 which extend axially along the length of each roller (see FIG. 6),preferably, at a peripheral end thereof. The rings 182 define cammingsurfaces 182 a which are engaged by the threaded bore 180 of thearmature drive cylinder 174 to move the output shaft 164 along thethreaded bore 180 in response to the rotation of the armature drivecylinder 174. The length of the threaded bore 180 within the armaturedrive cylinder 174 defines a track along which the transmission rollers166 of the actuator assembly 36 a move.

As set forth below, a portion of the output shaft 164 includes a cammingsurface 184 a shown in the form of corresponding annular grooves 184which are engaged by the annular rings 182 and camming surfaces 182 a ofthe transmission rollers 166 to advance the output shaft 164. Thus, asdescribed, when the armature drive cylinder 174 is selectively rotated(clockwise or counterclockwise) by the stator 170, the threaded bore 180engages the transmission rollers 166 to selectively move thetransmission rollers 166 along the threaded bore 180 of the armaturedrive cylinder 174. The annular rings 182 of the transmission rollers166 engages the annular groove 184 and camming surfaces 184 a of theoutput shaft 164 to move the output shaft 164.

The thread engaging portion of the actuator assembly 36 a (as defined bythe annular rings 182 of the transmission rollers 166) is significantlyshorter than the extent of the internal threads of the threaded bore 180within the armature drive cylinder 174 such that the difference betweenthem defines a maximum actuation stroke 186. Since the extent of thethread engaging portion (annular rings 182 of the transmission rollers166) is significantly small as compared to the extent of the threadswithin the armature drive cylinder 174 and since the motor assembly ispositioned around the output shaft 164, the length of the cylinder 174closely approximates the maximum extent of the actuation stroke 186 andthe length of the actuator assembly 36. Also, the thread engagingportion (annular rings 182 of the transmission rollers 166) and theannular rings 184 of the actuator assembly 36 a are maintained withinthe armature drive cylinder 174 during the entire actuation stroke 186.Thus, the interactive parts of the actuator assembly 36 a areself-protected during the entire stroke of the output shaft 164. Inaddition, since only a “smooth” portion of the output shaft 164 whichterminates into the pin 32 extends outside the threaded bore 180, aforward end of the bore 180 can be easily sealed to define a protectedchamber for the interacting elements of the device.

As illustrated in FIG. 5, at least three transmission rollers 166 areused. The transmission rollers 166 are mounted for rotation about theoutput shaft 164 and include forward and rear support axle extensions188 and 190 which cooperate with forward and rear support rings 192 and194, respectively (FIGS. 5 and 6). Each of the forward and rear supportrings 192 and 194 include support holes 196 which accept one of theextensions 188, 190. The number of support holes 196 on each of theforward and rear support rings 192 and 194 corresponds to the number oftransmission rollers 166. The forward support axle extensions 188 ofeach of the transmission rollers 166 extend through a support hole 196of the forward support ring 192. Likewise, the rear support axles 190 ofeach of the transmission rollers 166 extend through a support hole 196of the rear support ring 194. Thus, the forward and rear support rings192 and 194 maintain the spacing of the transmission rollers 166 aboutthe output shaft 164 during operation. The axle extensions 188 and 190are secured within the holes 196 of support rings 192 and 194 in anyknown manner.

As shown in FIG. 4, the housing assembly 172 includes a cylindrical tube198, an end cap 200, and a circular end seal 202. The end cap 200 ismounted to a first end of the cylindrical tube 198 by bolts 204 and thecircular end seal 202 is mounted to a second end of the cylindrical tube198, as by a proper fit.

The stator 170 of the motor assembly 168 is mounted about an innersurface of the cylindrical tube 198. The armature drive cylinder 174 isrotationally supported relative to the housing assembly 172 by front andrear bearings 206 and 208, respectively. The rear support bearing 208 ismounted to an internal surface of the circular end seal 202 torotationally support a rear portion of the armature drive cylinder 174.The circular end seal 202 includes a circumferential groove 210 withinwhich is maintained a retaining ring 212. A bumper 214 is interposed andheld in place between the retaining ring 212 and the bearing 208 toabsorb energy when the actuator assembly 36 a reaches the retractedposition at the rear end of the threaded bore 56 thereof. The circularend seal 208 includes a wire opening 216 for electrically connecting theexternal control 178 to the stator 170.

The end cap 200 is formed as a stepped cylindrical member having astepped central bore defining a first bore portion 218 and a second boreportion 220, the diameter of the first bore portion 218 being largerthan the diameter of the second bore portion 220. The front bearing 206is mounted within the first bore portion 218 of the end cap 200 torotationally support a front portion of the armature drive cylinder 174.The end cap 200 includes a circumferential groove 222 which maintains afront retainer ring 224 to secure the front bearing 206 relative to thehousing assembly 172.

The second bore portion 220 of the end cap 200 is internally threaded.An externally threaded tubular bushing support 226 is seated within theinternally threaded second bore portion 220 of the end cap 200. Thebushing 228 is concentrically positioned within the bushing support 226to support the output shaft 164 at a forward (output) end of the housingassembly 172. A ring seal 230 is included at a forward end of thebushing 228. The end cap 200 includes a flange portion 232 having screwholes 234 for attachment to the manifold 20. The screw holes 234 areused for receiving fasteners 51 a for fastening the flange portion 232along with the plate 47 to the manifold 20. Once again, the locator 48is located in the recess 50 of the manifold 20, correctly positioningthe actuating assembly 36

FIGS. 7-9 illustrate another preferred embodiment of a linear actuatorassembly 36 b in accordance with the present invention. As shown, inFIGS. 7-9, the linear actuator 36 b is similar to the embodimentdescribed in FIGS. 4-6, and has many of the same components. Thereference numbers used in FIGS. 4-6 are used to identify like componentsin FIGS. 7-9. As shown in FIGS. 7-9, actuator assembly 36 b differs fromthe embodiment of FIGS. 4-6 in that the transmission rollers 166 of theactuator assembly 36 b include forward and rear gear teeth 236 and 238.Further, the output shaft 164 (about which the transmission rollers 166are positioned) includes forward and rear gear teeth 240 and 242,respectively. The forward and rear gear teeth 236 and 238 of thetransmission rollers 166 mesh with the respective forward and rear gearteeth 240 and 242 of the output shaft 164 to maintain the relativeposition of the rollers 166 while the output shaft 164 moves along thethreaded bore 180 of the armature drive cylinder 174. The interaction ofthe gear teeth 236, 238 of the transmission rollers 166 and the gearteeth 240, 242 of the output shaft 164 prevents slippage therebetween.

FIGS. 10 and 11 illustrate a further embodiment of the actuator assembly36 c in accordance with the present invention. The actuator assembly 36c is similar to the embodiment shown in FIGS. 7-9, and, as such, likenumbers have been used to identify like parts. However, in the actuatorassembly 36 c of FIGS. 10 and 11, the camming surfaces of thetransmission rollers 166 are defined by threads 244 instead of annularrings as shown in the embodiments shown in FIGS. 4-9. Likewise, theportion of the output shaft 164 (about which the transmission rollers166 are spaced) includes threads 246 instead of annular rings as in theembodiments of FIGS. 4-9 which are engaged by the threads 244 of thetransmission rollers 166. In operation, the threads of the bore 180 ofthe armature drive cylinder 174 engage the threads 244 of thetransmission rollers 166 to move the transmission rollers 166 onrotation of the cylinder 174. The threads 244 of the transmissionrollers 166 likewise engage the threads 246 of the output shaft 164 tocorrespondingly move the output shaft 164 in cooperation with thetransmission rollers 166.

It will be appreciated by those skilled in the art that an objective ofthe actuator assemblies 36 a,36 b,36 c,36 d is to precisely apply linearmotion to some object or mechanism for controlling the valve gateopenings 18. The motion is generally programmed or defined in a computerprogram developed by the user of the actuator assembly 36 a,36 b,36 c,36d. For example, prior to using the actuator assembly 36 a,36 b,36 c,36d, the user enters the instructions and motion profiles into aprogrammable motion controller. The motion controller, when commanded,executes the user's program by signaling a servo amplifier to apply avoltage across the actuator's stator leads. The level of voltage appliedis a function of the velocity specified in the user's program for thespecific move being executed. The voltage causes current to flow in thestator windings of the actuator assembly 36 a,36 b,36 c,36 d which, inturn, applies a torque to the motor armature. In the actuator assembly36 a,36 b,36 c,36 d, the subsequent rotation of the armature isconverted mechanically within the actuator assembly 36 a,36 b,36 c,36 dto a linear motion reflected on the output shaft 164.

Specific instructions for both instantaneous position and velocity aretransmitted by the motion controller for each move executed. Inresponse, the amplifier applies a voltage level which represents anexpected velocity output of the actuator. The expected voltage/velocityrelationship is established by the user during setup and calibration ofthe system. Thus, typically the pin 32 position with respect to the gate30 can be precisely controlled via pre-calibration. Thus, it is notnecessary for closed loop control to be used in the present invention.In certain situations, the actual velocity of the output shaft 164 maynot exactly match what is being commanded by the motion controller. Ifdesired, the actual movement of the actuator output shaft can bemonitored to assure that the actuator produces the exact motion desired.In such a situation, a closed loop feed back control can be used in analternate embodiment.

In the present invention, this is accomplished by first incorporating avelocity/position feedback sensor 248 within the actuator assembly 36 d(best seen in FIG. 13) and second, by designing the servo amplifier 250and the controller 252 (best seen in FIG. 12) such that continuousadjustments are made to the voltage applied in response to any sensederror in position and/or velocity. By doing so, continual adjustment ofthe system command is accomplished such that the motion produced isexactly as intended by the user. For example, if the actuator assembly's36 d output during a particular movement is 0.100 inches behind thetarget position at that moment and/or it is moving too slow relative tothe instructions in the user program, then the voltage will be increasedslightly to increase its speed (i.e., the controller 252 attempts toeliminate the gap between the target and actual values).

The controller 252 must receive information as to the velocity and theposition of the actuator assembly's 36 d output shaft 164 at all times.A previous method of deriving this information was to utilize a linearposition sensor. Such sensors exist in many forms and includepotentiometers, LVDTs or magnostrictive types. While the accuracy of thefeedback sensor may vary without affecting control, the velocityfeedback must be continuous and linear with respect to the voltageapplied in order for the system to operate correctly. Likewise, therelationship between the armature's movement and the sensed positionmust be continuous and linear to operate correctly. However, in anyscrew style rotary-to-linear conversion mechanism a small amount ofbacklash exists, introducing error in these systems.

Backlash results from the fact that no mechanism can be manufacturedwhere all the components mesh or fit perfectly (i.e., tolerances arenear or are zero). Even if the components could fit perfectly, and evenassuming minimal wear, backlash would evolve. In the present case, itwill be appreciated that backlash causes a non-linearity ordiscontinuity in the above described relationships at that point wherethe torque being applied to the armature changes direction.

Any discontinuity in these relationships will confuse the controller tothe extent that instability or oscillation will occur. Therefore, thepoint at which the greatest precision and highest stability is normallydesired is also exactly the point where instability will most likelyoccur. More specifically, the motor servo-controller must accuratelyhold the desired output shaft position by applying forward or reversemovement or force in response to any sensed movement from the desiredposition. However, due to the tolerances that backlash creates there isa discontinuity between the application of forward and reverse movement.As a result, the controller causes the linear actuator to hunt, oroscillate, back and forth in an attempt to maintain it in a final targetposition.

One approach to solving this problem is to eliminate backlash. Thismight be done by splitting one or more of the roller screw components inhalf, and then preloading the pieces against each other by an adjustablespring mechanism. If this approach is utilized, it will be appreciatedthat the spring tension must then exceed the actuator's load capacity.

However, such an approach is expensive and takes up additional space.Further, only half of the screw mechanism carries the load. While thisapproach can be made to work, the additional friction resulting from thehigh forces applied substantially reduces the system'sefficiency—thereby increasing its power consumption thus reducing thelife of the unit correspondingly.

Turning to the present invention, since the position and velocity of theoutput shaft 164 is a known fixed ratio of the rotation of the armature,the preferred solution is to measure its rotational position andvelocity and allow the motion controller 252 to calculate the resultingposition of the actuator assembly's 36 output shaft 164. While backlashwill allow some back and forth movement of the output shaft 164, whenthe armature is held in position, no discontinuity between the voltageapplied to the armature and feedback will occur. Therefore, in thepreferred embodiment, the feedback sensor 248 is mounted directly andrigidly to the armature resulting in stable operation. Using thismethod, the amount of backlash must only be less than the systemaccuracy requirements of the application (i.e., the inaccuracy allowedmust be greater than the total backlash of the converting mechanism).

In an alternate embodiment, a rotary position/velocity sensor is used asillustrated in FIG. 12. Advantages associated with use of such a rotaryfeedback compared to a linear sensor device are that it is generallyless expensive; it is more rugged; it does not require expensive boringof the output shaft; it mounts conveniently at the rear end of thearmature; and it can be used to provide commutation signals required forbrushless motors. Alternatively, employing a linear sensor would requirethe use of a separate motor commutation sensor.

It will be appreciated that the system normally includes some form of aproportional, integral, derivative control process equation. However,those skilled in the art will appreciate that other control equations,such as proportional, proportional-derivative, fuzzy logic, etc. andother types of control devices may also be used. For a more detaileddiscussion, reference may be had to Dorf, Modern Control Systems, pages379 et. seq. (1981). Control equation constants for the preferredembodiment of the present system control, may be derived empirically,and may be changed depending upon the desired application. Additionally,those skilled in the art will appreciate that the constants may also bederived by determination of the transfer function from the steady-stateresponse or other such methods as are well known in the art.

By using the servo-amplifier 254 and controller 252, the linearpositioning of the output shaft 164 may be properly and quicklymaintained for predetermined target locations. As seen in FIG. 12,control is established by the angular position control of the rotarysensor 256 which is provided to the controller 252. The controller 252operates in accordance with its programmed position control profile andother programming steps, and provides signals to the servo amplifier254. In turn, the servo amplifier 254 provides the required voltage tothe linear actuator stator 170.

In the preferred embodiment, the rotary sensor 256 is an optical digitalencoder manufactured by Renco Corporation of California, under modeldesignation RHS25D. Such devices generally operate by utilizing a lightemitting device and a disk having a plurality of alternating opticallytransparent and opaque areas defined about the periphery. Thus, as thearmature rotates, the light is alternatingly blocked and allowed to passthrough the disk. A light sensitive device receives the light andprovides a signal indicative of the light intensity received by thelight sensitive device. It will be appreciated, however, that a lightemitting device and a light receiving device together form an opticalsensor, and that analog generators may also be utilized as part of thesystem.

One example of this type of system is shown in FIG. 12. As seen in FIG.12, a valve gate assembly constructed in accordance with the principlesof the present invention includes an actuator assembly 36 as describedabove and still includes the pin 32 as described above. This embodimentalso includes a master controller device 254 receives signals fromsensors (not shown) via the signal path 256 to positively confirm thepin 32 operation and/or the flow of fluid/materials to mold 14.

Through use of the system described above, as well as timing themovement of the pin 32 via master controller 254, the timing andprogramming of the entire valve gate assembly 10 may be controlled. Forexample, master controller 254 may provide instructions or interruptsignals to controller 252 via signal path 258. In turn controller 252provides a signal to the servo amplifier 250 via signal path 260. Thissignal is preferably a signal as discussed above (i.e., the signalincludes an output signal generated from the desired position of theoutput shaft compared to the position of the output shaft determined byrotational position sensor 248). The servo amplifier 250 provides theproper voltage to the linear actuator via signal path 262. It will beappreciated by those skilled in the art that the controller 252 andservo amplifier 250 comprise the external controller referenced above.The output signal of the rotational position sensor 248 is provided tothe controller via signal path 264. In this manner, a precise deliveryof fluid/materials is accomplished.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail. For example, the output shaft“164” may be formed with rings or threads which directly engage thethreads of the threaded bore 180 of the armature drive cylinder 174.Analog or digital sensors may be employed to detect the position of theoutput shaft, that information being used in control systems of knowndesign. Also, other motor designs and types may be adapted to thepractice of the present invention. These and other changes within thescope of the appended claims are anticipated by the present invention.

The present invention has been described in an illustrative manner. Itis to be understood that the terminology, which has been used, isintended to be in the nature of words of description rather than oflimitation.

Many modifications and variations of the present invention are possiblein light of the above teachings. Therefore, within the scope of theappended claims, the present invention may be practiced other than asspecifically described.

1. A valve gate assembly for an injection molding machine, comprising: avalve operably associated with a valve gate of an injection moldingmanifold; an actuator assembly operably coupled to said valve; and anaxially movable output shaft in substantial axial alignment with saidvalve, said actuator assembly coupled to said axially moveable outputshaft through a transmission assembly, such that said actuator assemblytranslates motion to said output shaft and said valve through the use ofsaid transmission assembly for driving said valve and opening said valvegate, said actuator assembly operable for providing movement of saidvalve between an open position and a closed position, and stopping saidvalve at any position therebetween.
 2. The valve gate assembly of claim1, wherein said valve further comprises: at least one pin disposedwithin at least one flow passage at said valve gate, said at least onepin having an end disposed within said gate, and another end connectedto said actuator assembly, said flow passage larger in diameter thansaid at least one pin; and wherein said output shaft of said actuatorassembly selectively moves said pin in said flow passage to allow moltenmaterial through said gate into a mold cavity.
 3. The valve gateassembly of claim 1, wherein said actuator assembly further comprises:an outer member comprising an elongated cylinder disposed within ahousing, said elongated cylinder having a threaded bore and being madeof a magnetic material and supported for rotation in said housing; astator mounted in said housing, said stator circumscribing at least aportion of said elongated cylinder; at least one magnet disposed on saidelongated cylinder, operably associated with said stator; a portion ofsaid valve terminating into said output shaft, said output shaftdisposed within said elongated cylinder, and a portion of said outputshaft having a camming surface; said transmission assembly including aplurality of transmission rollers having camming surfaces which arereceived by said camming surface of said output shaft and said threadedbore of said elongated cylinder; and wherein when the stator isactivated, said stator will cause said at least one magnet and saidelongated cylinder to rotate, thereby causing said plurality oftransmission rollers to engage and translate along said threaded bore,said plurality of transmission rollers engaging said camming surface ofsaid output shaft facilitating translation of said output shaft relativeto said output shaft in said elongated cylinder.
 4. The valve gateassembly of claim 3, wherein said actuator assembly further comprises:each of said plurality of transmission rollers having a forward supportaxle extension and a rear support axle extension; a forward support ringhaving a plurality of support holes for receiving said forward supportaxle extensions of each of said plurality of transmission rollers; arear support ring having a plurality of support holes for receiving saidrear support axle extensions of each of said plurality of transmissionrollers; and wherein said forward support ring and said rear supportring properly space said plurality of transmission rollers about saidoutput shaft.
 5. The valve gate assembly of claim 3, further comprising:said plurality of transmission rollers having forward gear teeth andrear gear teeth; said output shaft having forward gear teeth and reargear teeth in mesh with said forward gear teeth and said rear gear teethof said plurality of transmission rollers; and wherein said forward gearteeth and said rear gear teeth of said plurality of transmission rollersare in mesh with said forward gear teeth and said rear gear teeth ofsaid output shaft and maintain the relative position of said pluralityof transmission rollers relative to said output shaft as said outputshaft translates in said threaded bore.
 6. The valve gate assembly ofclaim 3, wherein said camming surface of said output shaft is oneselected from the group comprising annular rings, annular ribs, orsurface forming annular grooves in said output shaft.
 7. The valve gateassembly of claim 3, wherein said camming surface of said plurality oftransmission rollers is a slated surface of said rollers.
 8. The valvegate assembly of claim 1, wherein said actuator assembly is controlledby a closed-loop feedback control system.
 9. The valve gate assembly ofclaim 8, said closed-loop feedback control system comprising: a mastercontroller for detecting the position of said valve; a rotary positionsensor for detecting the position of said actuator assembly, anddelivering the position of said actuator assembly to a controller; andwherein said master controller will receive the position of said valveand the position of said actuator from said controller, and command saidcontroller to change the position of said actuator assembly when theposition of said valve does not match the commanded position deliveredto said actuator assembly from said controller.
 10. The valve gateassembly of claim 1, wherein said actuator assembly is operable to movesaid valve incrementally between said open position and said closedposition.
 11. The valve gate assembly of claim 10, wherein said actuatoris operable to move said valve in approximately 0.001 inch incrementsbetween said open position and said closed position.
 12. The valve gateassembly of claim 1, wherein the distance said actuator moves said valvebetween said open position and said closed position is approximately oneinch.
 13. A valve gate assembly for an injection molding machine,comprising: a valve gate having a valve operable for being moved betweena fully open position and a fully closed position to control themovement of a flowable material into a cavity; an axially movable outputshaft in substantial axial alignment with said valve; and an actuatorassembly coupled to said axially movable output shaft through atransmission assembly, wherein said transmission assembly translatesrotary motion of said actuator assembly to linear motion of said outputshaft for driving said valve and opening said valve gate, and saidactuator assembly operable for providing movement of said valve betweensaid fully open position and said fully closed position, and stoppingsaid valve at any position therebetween.
 14. The valve gate assembly foran injection molding machine of claim 13, said valve further comprisinga pin disposed within a flow passage, at least a portion of said flowpassage being larger in diameter than said pin.
 15. The valve gateassembly for an injection molding machine of claim 13, wherein saidactuator assembly is controlled by a closed-loop feedback system. 16.The valve gate assembly for an injection molding machine of claim 15,said closed loop feedback system further comprising: at least onesensor; and a controller, said at least one sensor electricallyconnected to said controller for controlling said valve, wherein saidcontroller commands said actuator assembly to move said valve to aspecific position, and the position and velocity of said valve ismeasured to allow said controller to calculate the resulting position ofsaid valve.
 17. The valve gate assembly for an injection molding machineof claim 16, said at least one sensor operable for detecting the flow ofmolten material into said cavity.
 18. The valve gate assembly for aninjection molding machine of claim 16, said at least one sensor furthercomprising a feedback sensor operable for detecting the velocity andposition of said valve, and communicating the velocity and position ofsaid valve to said controller.
 19. The valve gate assembly for aninjection molding machine of claim 18, wherein said feedback sensorprovides substantially continuous and substantially linear feedback ofthe velocity of said valve to said controller.
 20. The valve gateassembly for an injection molding machine of claim 13, wherein saidactuator assembly is one selected from the group consisting of a linearmotor, a brushless direct current (DC) motor, linear synchronous motor,linear drive, linear servo, and a linear tubular motor.
 21. The valvegate assembly for an injection molding machine of claim 13, wherein therange of movement of said valve between said fully open position andsaid fully closed position is approximately one inch.
 22. The valve gateassembly for an injection molding machine of claim 13, wherein saidactuator assembly is operable to move said valve incrementally.
 23. Thevalve gate assembly for an injection molding machine of claim 22,wherein said actuator assembly is operable to move said valve inincrements of 0.001 inch.
 24. A valve gate assembly for an injectionmolding machine, comprising: a valve operable for opening an closing avalve gate, said valve being moved incrementally between an openposition and a closed position; an actuator assembly having an axiallymovable output shaft operable for moving said valve; a transmissionassembly operable for translating rotary motion of said actuator tolinear motion of said output shaft for driving said valve and openingsaid valve gate; and a pin formed as part of said valve for allowing orpreventing the flow of molten material through said valve gate, saidaxially movable output shaft in substantial axial alignment with saidvalve.
 25. The valve gate assembly for an injection molding machine ofclaim 24, said valve being operable for movement in increments of 0.001inch.
 26. The valve gate assembly for an injection molding machine ofclaim 24, wherein the distance between said fully open position and saidfully closed position is approximately one inch.
 27. The valve gateassembly for an injection molding machine of claim 24, furthercomprising a flow passage, wherein said pin is at least partiallydisposed in said flow passage, and at least a portion of said flowpassage is larger in diameter than said pin.
 28. The valve gate assemblyfor an injection molding machine of claim 24, wherein said actuatorassembly is controlled by a closed loop feedback system, comprising: aplurality of sensors, one of said plurality of sensors being operablefor detecting the flow of molten material into said cavity; and acontroller operable for receiving a signal from one or more of saidplurality of sensors.
 29. The valve gate assembly for an injectionmolding machine of claim 28, one of said plurality of sensors furthercomprising a feedback sensor, said feedback sensor being operable fordetecting the velocity and position of said valve, and communicating thevelocity and position of said valve to said controller, wherein saidfeedback sensor provides substantially continuous and substantiallylinear feedback of the velocity of said valve to said controller. 30.The valve gate assembly for an injection molding machine of claim 24,said actuator assembly being operable to move said valve incrementallyin 0.001 inch increments.
 31. The valve gate assembly for an injectionmolding machine of claim 24, wherein the range of movement of said valvebetween said fully open position and said fully closed position isapproximately one inch.
 32. The valve gate assembly for an injectionmolding machine of claim 24, wherein said actuator assembly is oneselected from the group consisting of a linear motor, a brushless directcurrent (DC) motor, linear synchronous motor, linear drive, linearservo, and a linear tubular motor.